Municipal solid waste (MSW) reflects the culture that produces it and affects the health of the people and the environment surrounding it. Globally, people are discarding growing quantities of waste, and its composition is more complex than ever before, as plastic and electronic consumer products diffuse. Concurrently, the world is urbanizing at an unprecedented rate. These trends pose a challenge to cities, which are charged with managing waste in a socially and environmentally acceptable manner. Effective waste management strategies depend on local waste characteristics, which vary with cultural, climatic, and socioeconomic variables, and institutional capacity. Globally, waste governance is becoming regionalized and formalized. In industrialized nations, where citizens produce far more waste than do other citizens, waste tends to be managed formally at a municipal or regional scale. In less-industrialized nations, where citizens produce less waste, which is mostly biogenic, a combination of formal and informal actors manages waste. Many waste management policies, technologies, and behaviors provide a variety of environmental benefits, including climate change mitigation. Key waste management challenges include integrating the informal waste sector in developing cities, reducing consumption in industrialized cities, increasing and standardizing the collection and analysis of solid waste data, and effectively managing increasingly complex waste while protecting people and the environment.

Soil organic matter (SOM) supports the Earth's ability to sustain terrestrial ecosystems, provide food and fiber, and retains the largest pool of actively cycling carbon.Over 75% of the soil organic carbon (SOC) in the top meter of soil is directly --

Direct emissions from commercial-scale composting are uncertain. We used micrometeorological methods to continuously measure greenhouse gas (CO 2 , CH 4 , N 2 O) emissions from full composting of green waste and manure. We measured oxygen (O 2 ), moisture, and temperature continuously inside the composting pile, and analyzed chemical and physical characteristics of the feedstock weekly as potential drivers of emissions. Temperature, moisture, and O 2 all varied significantly by week. Feedstock porosity, C:N, and potential N mineralization all declined significantly over time. Potential net nitrification remained near zero throughout. CH 4 and CO 2 fluxes, indicators of feedstock lability, were variable, and most emissions (75% and 50% respectively) occurred during the first three weeks of composting. Total CH 4 emitted was 1.7±0.32 g CH 4 kg −1 feedstock, near the median literature value using different approaches (1.4 g CH 4 kg −1 ). N 2 O concentrations remained below the instrument detection. Oxygen, moisture and temperature exhibited threshold effects on CH 4 emissions. Net lifecycle emissions were negative (−690 g CO 2 -e kg −1 ), however, after considering avoided emissions and sinks. Managing composting piles to minimize methanogenesis-by maintaining sufficient O 2 concentrations, and focusing on the first three weeks-could reduce emissions, contributing to the climate change mitigation benefit of composting.

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Biomass can help reduce greenhouse gas (GHG) emissions by displacing petroleum in the transportation sector, by displacing fossil-based electricity, and by sequestering atmospheric carbon. Which use mitigates the most emissions depends on market and regulatory contexts outside the scope of attributional life cycle assessments. We show that bioelectricity's advantage over liquid biofuels depends on the GHG intensity of the electricity displaced. Bioelectricity that displaces coal-fired electricity could reduce GHG emissions, but bioelectricity that displaces wind electricity could increase GHG emissions. The electricity displaced depends upon existing infrastructure and policies affecting the electric grid. These findings demonstrate how model assumptions about whether the vehicle fleet and bioenergy use are fixed or free parameters constrain the policy questions an analysis can inform. Our bioenergy life cycle assessment can inform questions about a bioenergy mandate's optimal allocation between liquid fuels and electricity generation, but questions about the optimal level of bioenergy use require analyses with different assumptions about fixed and free parameters.